Announcer: Frank Acinapura has lived with Paget's disease for most of his adult life. A veteran of World War II, an officer at the United Nations, Frank had a typical, but frequently overlooked clue. His hats weren't really shrinking.

Frank Acinapura: And I always wanted a Barcelonian hat. So, I bought one and it fit me just beautiful. And it was in January on 1950, and I thought, "Boy, when I go to church on Easter Sunday with a hat like that, all the other friends would be envious of me."

But when Easter came around, three or four months later, after buying it, I never wore it -- I put it on my head and it did not fit me.

Announcer: No one suspected Paget's though. A stomach problem seven years later led to a spinal x-ray. And then, Paget's was diagnosed. While it's considered a relatively rare disease, Paget's has probably been around for thousands of years.

What actually happens to bone in Paget's disease?

Frederick Singer, M.D.: In normal bone, there is a process of breakdown and formation of bone. In Paget's disease, this goes awry and there's an acceleration of the bone breakdown at first. But after many years, there's an overgrowth of bone and it is abnormal bone, which is prone to fracture.

Announcer: Although relatively uncommon, Paget's is actually the second most prevalent bone disease after osteoporosis. But the diseases are fundamentally different.

Ethel Siris, M.D.: In osteoporosis, the problem is that as people age there is generally more bone being removed than is being put back. And the bone becomes thinner and thinner.

In Paget's disease there's a lot of bone being removed, but there's a lot of bone being made. And the problem there is that the bone is thicker. It's actually bigger, which is why it takes more space and therefore can pinch nerves or cause the skull to become thick.

Announcer: While Paget's disease can affect any bone in the body, its clinical impact depends on which bones in the body are affected. Some common sites are the skull, where enlarged bone can lead to headache and hearing loss.

The spine, where Paget's can cause vertebrae to collapse and compress the spinal cord and nerves sometimes leading to neurological problems. Paget's disease in the pelvis can cause serious hip problems, especially in the joints, which may lead to immobility and the need for hip replacement surgery.

In the lower limbs, Paget's may result in bowed legs, difficulty walking and pain in the ankle, knee and hip joints. Although sometimes causing no symptoms, Paget's disease can cause bone pain, arthritis, noticeable deformities and fracture. And Paget's can certainly impact quality of life.

Frederick Singer, M.D.: Paget's disease can produce a devastating effect on a patient's life, simply because their body changes. Sometimes the patient has great difficulty in doing the usual daily tasks of life.

Announcer: For more than 40 years, Frank Acinapura has taken health matters into his own hands, determined to live a normal and active life despite Paget's.

Frederick Singer, M.D.: We have made tremendous progress in the past 25 years or so. Before then, we had no real idea of what might be the cause of Paget's disease. And, now we are working hard on this problem. Even more importantly, we now have extremely effective treatments for Paget's disease.

Ethel Siris, M.D.: Mr. Acinapura really exemplifies the ideal attitude that an individual needs to have with this condition. First of all, when he found out he had a problem, he sought medical help. And he sought someone who he thought was going to know a great deal about it. In addition, he's got an incredibly positive attitude.

Frank: There is a reason that I have lived all these experiences and beat that. So, maybe, it is to help other people.